Bidirectional transmittance of transparent windows with external or backside condensation of nonabsorbing cap-shaped droplets

•Systematic study of bidirectional transmittance of windows with droplets on its front or back.•Transmittance was independent of droplet size distribution and spatial arrangement.•Transmitted photons were concentrated in angular region bounded by cutoff angles.•Analytical expressions of cutoff angles agreed well with numerical simulations.•Bidirectional transmittance away from incident direction increased with surface area coverage.